MNRAS 453, 2885–2900 (2015) doi:10.1093/mnras/stv1809
Gone without a bang: an archival HST survey for disappearing massive stars
Thomas M. Reynolds,1,2‹ Morgan Fraser1 and Gerard Gilmore1 1Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK 2Tuorla Observatory, Department of Physics and Astronomy, University of Turku, Vais¨ al¨ antie¨ 20, FI-21500 Piikkio,¨ Finland Downloaded from Accepted 2015 August 4. Received 2015 July 16; in original form 2015 May 27
ABSTRACT
It has been argued that a substantial fraction of massive stars may end their lives without http://mnras.oxfordjournals.org/ an optically bright supernova (SN), but rather collapse to form a black hole. Such an event would not be detected by current SN surveys, which are focused on finding bright transients. Kochanek et al. proposed a novel survey for such events, using repeated observations of nearby galaxies to search for the disappearance of a massive star. We present such a survey, using the first systematic analysis of archival Hubble Space Telescope images of nearby galaxies with the aim of identifying evolved massive stars which have disappeared, without an accompanying optically bright SN. We consider a sample of 15 galaxies, with at least three epochs of Hubble Space Telescope imaging taken between 1994 and 2013. Within this data, we find one candidate at CERN - European Organization for Nuclear Research on September 15, 2016 which is consistent with a 25–30 M yellow supergiant which has undergone an optically dark core-collapse. Key words: stars: evolution – stars: massive – supernovae: general.
plosion, and Type IIL (Linear) SNe which have a steady decline 1 INTRODUCTION in luminosity from peak. These differing SN types have long been Massive (>8M ) stars end their lives as core-collapse supernovae believed to result from the extent of the H and/or He envelope of (CCSNe). Once they have evolved off the main sequence and de- the progenitor star at the moment of collapse (Falk & Arnett 1977), veloped a Chandrasekhar-mass Fe core, the pressure in their core is although recently there has been some debate in the literature as to no longer sufficient to support the star against its own gravity. The whether Type IIP and IIL SNe are distinct classes (e.g. Anderson inner core begins to infall, a process which is halted once it reaches et al. 2014; Faran et al. 2014, and references therein). nuclear densities and forms a protoneutron star (PNS). At this point Nearby CCSNe present a unique opportunity to test this hy- the core rebounds and drives a shock outwards through the star. pothesis by directly identifying their massive stellar progenitors in According to current simulations, this shock lacks the energy to archival images. This was first accomplished for SN 1987A in the halt the stars collapse and explode the outer layers of the star. It is Large Magellanic Cloud (LMC; West et al. 1987), and for SN 1993J believed that the deposition of additional energy behind the shock in M51 (Aldering, Humphreys & Richmond 1994; Maund & Smartt (perhaps in the form of neutrinos) can revive it and cause the star to 2009). Since then, there has been significant success in detecting the explode as a CCSNe (e.g. Janka et al. 2007; Burrows 2013). If the H-rich progenitors of Type II SNe (e.g. Li et al. 2007; Mattila et al. energy deposition is insufficient, then the shock is not revived and 2008; Maund et al. 2011; Van Dyk et al. 2012;Fraseretal.2014). In instead the outer layers of the star collapse on to the PNS, forming a particular, Type IIP SNe have been shown to come from red super- black hole (e.g. Woosley 1993;Fryer1999; O’Connor & Ott 2011). giants (RSGs) with extended atmospheres (Smartt et al. 2009). The This is a more likely outcome for more massive stars, which have H-poor progenitors of Type Ibc SNe, however, have thus far eluded bigger Fe cores and are consequently harder to explode. confirmed detections (Eldridge et al. 2013), with only iPTF13bvn SNe are distinguished primarily by the elements seen in their (Cao et al. 2013; Bersten et al. 2014; Eldridge et al. 2015)asa spectra – Type I SNe are H poor, while Type II SNe are H rich viable, albeit unconfirmed, candidate. (Filippenko 1997;Smartt2009). The Type I SNe are further sub- While statistical studies of ensembles of SN progenitors (Van divided into Type Ib and Type Ic SNe which show the presence Dyk, Li & Filippenko 2003;Smarttetal.2009) have revealed that or absence of He, respectively. H-rich Type II SNe are separated Type IIP SNe do indeed come from RSGs, there is an apparent lack according to their light curves into Type IIP (Plateau) SNe, which of progenitors with a luminosity comparable to that of the brightest show an extended period of roughly constant luminosity after ex- known RSGs. Smartt et al. found that there was a statistically signif- icant absence of higher mass (16 M ) RSGs exploding as SNe, terming this the ‘Red Supergiant Problem’. Smartt et al. went on to E-mail: thmire@utu.fi suggest that the RSG problem might be explained by failed SNe,